This invention arose from a need to move a spacecraft, traveling in a first orbit around a first body, into a second orbit around a second body, where a desired inclination plane for the second body may upon arbitrarily oriented. This problem arises in a proposed Dark Ages Radio Explorer (DARE) mission to study red-shifted radiation (21 cm wavelength; 40-120 MHz) from primeval neutral hydrogen atom transitions that may have occurred at a time adjacent to beginning of the universe after the Big Bang occurred. 80-420 million years after the Big Bang.
The Big Bang itself produced a universe that was initially hot, dense and relatively homogeneous. The universe cooled as it expanded; and a primordial plasma, estimated to have formed about 400,000 years after the Big Bang, produced energetic protons and electrons that later combined to provide neutral; hydrogen atoms and an optically thin “atmosphere.” Photons from this age experienced reduced interactions with matter. These photons have produced a cosmic microwave background (CMB) that is still present, but tenuous. Stars and galaxies later formed and flooded the universe with ultraviolet photons sufficiently energetic to (re)ionize most or all of the hydrogen molecules (15.43 eV for single ionization). A primary goal of the DARE mission is to measure the spectral shape (intensities and wavelengths) associated with creation of the first stars and black holes, through measurement of a 21-cm red-shifter signal over a specified radio bandpass of 40-120 MHz. The red shift of primary interest is 11-35 cm, which is believed to correlate with the period 80-420 million years after the Big Bang.
Measurement of the red-shifted emissions requires a relatively dark and stable environment and avoidance of direct illumination by FM radio sources on the Earth and on the Sun. Direct illumination of the Moon's surface by these FM sources is approximately 109 times as bright as the estimated intensity of the primordial emission signals that are sought by DARE. Measurements made on a portion of the far side of the lunar surface, which is not directly illuminated by the Sun's radio sources, may allow observations of the emissions that are not disturbed by the greater brightness.
A DARE observational vehicle was planned to orbit the Moon for about 3 years and accumulate relevant astronomical data exclusively on the lunar far side, when direct illumination by both the Sun and Earth is absent. Orbits inclined near the lunar equatorial and lunar orbit planes generally yield more cumulative observation time inside the aforementioned Sun and Earth shadow cones compared to significantly inclined orbits (e.g., polar). Although the DARE spacecraft's trajectory was designed to yield an equatorial lunar orbit, any inclination may be achieved using DARE's nominal trajectory. However, this invention focuses on the DARE transfer trajectory, from GTO to the lunar orbit plane and finally to lunar orbit, along with alternate methods to achieve lunar orbit.